SAE Paper 940376 describes a type of fuel/air ratio determining method. During the determination of a single cylinder lambda from the signal of the one exhaust gas probe evaluated with the aid of an inverted model, it has been shown in test stand experiments that there was good agreement of the results of the model and the actual values of lambda that occurred in the individual cylinders. However, when the model applied to one engine using a reference probe was transferred to other engines of the same type, greater deviations between the modeled lambda values and the measured lambda values showed up. In this context, faulty assignments were also noted. That means, the model did appear to deliver appropriate lambda values, but it associated these with the wrong cylinders.